:agree:Known car vrs unknown car.
As our cars age, there's no telling how someone did, or didn't take care of them.
When I shopped my car, I came across two that looked identical on paper: same year, same mileage, 98% same options. Both only 2 years old. But on inspection, the car I didn't choose had mold in the trunk and interior, interior plastics in pretty bad shape and, without more technical evidence, "drove funny." All that only suggests how they did or didn't maintain the stuff I couldn't see. Price difference? $1,000 more for the better-kept car.
I say keep what you have unless the offer is SO good that it would matter less that you ran into issues with a replacement (e.g., your $25k counter offer.) I would think you could probably get $16000 just selling it on autotrader.com.